An induction motor vector control for controlling a motor torque by adjusting a magnetic flux current and a torque current obtained by converting a three-phase alternating current caused to flow into a stator of an induction motor into currents in an orthogonal two-axis coordinate system synchronized with a power source angular frequency (=motor electric angular frequency+slip angular frequency) is disclosed on pages 72-98 of “Actual Theory and Design of AC Servo Systems” by Hidehiko Sugimoto, Masato Koyama and Shinzo Tamai. In the case of controlling the slip angular frequency in proportion to a ratio of the torque current and a rotor magnetic flux, an induction motor torque is proportional to the product of the rotor magnetic flux generated with a delay in response to an excitation current and the orthogonal torque current.
A vibration damping control apparatus for the synchronous motor described in JP2001-45613A calculates a drive torque target value (T1*) by filtering a drive torque request value (T*) through a vibration damping filter for suppressing the torsional vibration of a drive shaft of a vehicle. In this synchronous motor, a rotor magnetic flux is constantly generated by a permanent magnet provided in a rotor, and an output torque of a synchronous motor proportional to the product of the rotor magnetic flux, which is a fixed value, and a torque current becomes a linear response value and coincides with the above drive torque target value (T1*).
However, in the case of simply applying the vibration damping filter described in JP2001-45613A to a control system for an induction motor, the following problem occurs. Specifically, although the drive torque target value obtained by applying the vibration damping filter to the drive torque request value is a target value capable of reducing torsional vibration, it does not coincide with the drive torque target value. This is because an output torque of the motor is a nonlinear response value due to a delay of the rotor magnetic flux in the induction motor. Thus, the torsional vibration of the drive shaft cannot be suppressed.
The present invention aims to provide an induction motor control apparatus capable of suppressing the torsional vibration of a drive shaft.
According the present invention, an induction motor control apparatus controls an induction motor connected to drive wheels by setting a motor torque command value on the basis of vehicle information. The induction motor control apparatus calculates a first torque current command value and a first excitation current command value on the basis of the motor torque command value and estimates a rotor magnetic flux on the basis of the first excitation current command value. The induction motor control apparatus calculates a first torque command value on the basis of an estimated value of the rotor magnetic flux and the first torque current command value. The induction motor control apparatus calculates a second torque command value by applying filter processing to the first torque command value, a natural vibration frequency component of a drive shaft torque transmission system in a vehicle being removed in the filter processing. Then the induction motor control apparatus controls drive of the induction motor on the basis of the first excitation current command value and the second torque current command value.
Embodiments of the present invention are described in detail below with reference to the accompanying drawings.